/* html 看不到， css inherit 继承 */
*{
    margin: 0;
    padding: 0;
}
html {
    height:100%;
    font-size: 10px;  
    background: url('./background.jpg') bottom center;
    background-size:cover;
    font-family: sans-serif;
}

.keys{
    display:flex; /*弹性布局*/
    /* flex-direction: column; */
    flex:1;
    min-height:100vh; /*vh viewportHeight 相等单位,设备无关性的px是绝对单位*/
    /* background-color: aqua;   前端调试的法宝 */
    align-items:center;
    justify-content: center;
}
.key{
    border:.4rem solid black;  /*rem 相对单位 相对html font-size*/
    border-radius: .5rem;
    margin:1rem;
    font-size:1.5rem;
    padding: 1rem 0.5rem;
    width:10rem;
    text-align: center;
    color:white;
    background-color: rgba(0,0,0,0.4);
    text-shadow: 0 0 0.5rem black;
}
.key>div {
    font-size:4rem;
}
.key .sound{
    text-transform: uppercase;
    font-size:1.2rem;
    letter-spacing: .1rem;
    color:#ffc600;
}
.playing {
    border-color:#ffc600;
    transform: scale(1.1); /*变形属性 scale 缩放 1.1倍*/
    box-shadow: 0 0 lrem #ffc600;
}